Leveraging knowledge generated in design activities for subsequent design and research purposes is an important yet challenging task due to the complex and messy nature of design work. In this paper, we discuss opportunities and challenges for documentation in design processes to support the transformation of design knowledge across different levels of abstraction. We argue for an activity-centred approach to underscore the construction of intermediate forms of knowledge, where immediate responses to design activities inform mediated representations of design work. The relation between immediate and mediated knowledge is explored through a case study of Co-notate, a research prototype enabling automatic synthesis of audio/video recordings and textual annotations simultaneously captured during design activities. We argue that real-time annotated design documentation limits the risk of recorded activities being misinterpreted, or simply disregarded, and we identify and discuss potentials for employing real-time technology to inform retrospective analysis.